High-temperature study of phase equilibria in the systems CsCl-LnCl(3) (Ln=Ce, Nd) by Knudsen effusion mass spectrometry

The vaporization of samples of different chemical and phase compositions in the systems CsCl-LnCl(3) (Ln=Ce, Nd) was investigated in the temperature r ange between 850 and 1050 K by the use of Knudsen effusion mass spectrometr y. The gaseous species CsCl, Cs2Cl2, LnCl(3), Ln(2)Cl(6) and CsLnCl(4) were identified in the vapour and their partial pressures were determined. The thermodynamic activities of CsCl, and LnCl(3) and the free enthalpies of fo rmation for the phases Cs(3)LnCl(6)(s) were determined at 950 K in the two phase fields {liquid+Cs(3)LnCl(6)(s)}. The correlations between the condens ed phase equilibria and the partial pressures of the vapour components at t he phase boundaries are discussed and illustrated with the present experime ntal data.